Stellarator

Example of a stellarator design, as used in the Wendelstein 7-X experiment: A series of magnet coils (blue) surrounds the plasma (yellow). A magnetic field line is highlighted in green on the yellow plasma surface.

The stellarator was invented by Lyman Spitzer of Princeton University in 1951, and much of its early development was carried out by his team at what became the Princeton Plasma Physics Laboratory (PPPL). The basic concept is to lay out the magnetic fields so that particles circulating around the long axis of the machine follow twisting paths, which cancels out instabilities seen in purely toroidal machines. This would keep the fuel confined long enough to allow it to be heated to the point where fusion would take place.

The first Model A started operation in 1953 and proved the basic layout worked. Larger models followed, but these demonstrated poor performance, suffering from a problem known as pump-out that caused them to lose plasma at rates far worse than theoretical predictions. By the early 1960s, any hope of quickly producing a commercial machine faded, and attention turned to studying the fundamental theory of high-energy plasmas. By the mid-1960s, Spitzer was convinced that the stellarator was matching the Bohm diffusion rate, which suggested it would never be a practical fusion device.

The release of information on the USSR's tokamak design in 1968 indicated a leap in performance. This led to the Model C stellarator being converted to the Symmetrical Tokamak (ST) as a way to confirm or deny these results. ST confirmed them, and large-scale work on the stellarator concept ended as the tokamak got most of the attention. The tokamak ultimately proved to have similar problems to the stellarators, but for different reasons. Since the 1990s, this has led to renewed interest in the stellarator design.[2] New methods of construction have increased the quality and power of the magnetic fields, improving performance. A number of new devices have been built to test these concepts. Major examples include Wendelstein 7-X in Germany, the Helically Symmetric Experiment (HSX) in the USA, and the Large Helical Device in Japan.

100 keV corresponds to a temperature of about a billion kelvins. Due to the Maxwell–Boltzmann statistics, a bulk gas at a much lower temperature will still contain some particles at these much higher energies. Because the fusion reactions release so much energy, even a small number of these reactions can release enough energy to keep the gas at the required temperature. In 1944, Enrico Fermi demonstrated that this would occur at a bulk temperature of about 50 million Celsius, still very hot but within the range of existing experimental systems. The key problem was confining such a plasma; no material container could withstand those temperatures. But because plasmas are electrically conductive, they are subject to electric and magnetic fields which provide a number of solutions.[5]

In a magnetic field, the electrons and nuclei of the plasma circle the magnetic lines of force. One way to provide some confinement would be to place a tube of fuel inside the open core of a solenoid. A solenoid creates a magnetic lines running down its center, and fuel would be held away from the walls by orbiting these lines of force. But such an arrangement does not confine the plasma along the length of the tube. The obvious solution is to bend the tube around into a torus (donut) shape, so that any one line forms a circle, and the particles can circle forever.[6]

However, this solution does not actually work. For purely geometric reasons, the magnets ringing the torus are closer together on the inside curve, inside the "donut hole". Fermi noted this would cause the electrons to drift away from the nuclei, eventually causing them to separate and cause large voltages to develop. The resulting electric field would cause the plasma ring inside the torus to expand until it hit the walls of the reactor.[6]

In the post-war era, a number of researchers began considering different ways to confine a plasma. George Paget Thomson of Imperial College London proposed a system now known as z-pinch, which runs a current through the plasma.[7] Due to the Lorentz force, this current creates a magnetic field that pulls the plasma in on itself, keeping it away from the walls of the reactor. This eliminates the need for magnets on the outside, avoiding the problem Fermi noted. Various teams in the UK had built a number of small experimental devices using this technique by the late 1940s.[7]

Another person working on controlled fusion reactors was Ronald Richter, a former German scientist who moved to Argentina after the war. His thermotron used a system of electrical arcs and mechanical compression (sound waves) for heating and confinement. He convinced Juan Perón to fund development of an experimental reactor on an isolated island near the Chilean border. Known as the Huemul Project, this was completed in 1951. Richter soon convinced himself fusion had been achieved in spite of other people working on the project disagreeing.[8] The "success" was announced by Perón on 24 March 1951, becoming the topic of newspaper stories around the world.[9]

While preparing for a ski trip to Aspen, Lyman Spitzer received a telephone call from his father, who mentioned an article on Huemul in the New York Times.[10] Looking over the description in the article, Spitzer concluded it could not possibly work; the system simply could not provide enough energy to heat the fuel to fusion temperatures. But the idea stuck with him, and he began considering systems that would work. While riding the ski lift, he hit upon the stellarator concept.[11][b]

The basic concept was a way to modify the torus layout so that it addressed Fermi's concerns though the device's geometry. By twisting one end of the torus compared to the other, forming a figure-8 layout instead of a circle, the magnetic lines no longer travelled around the tube at a constant radius, instead they moved closer and further from the torus' center. A particle orbiting these lines would find itself constantly moving in and out across the minor axis of the torus. The drift upward while it travelled through one section of the reactor would be reversed after half an orbit and it would drift downward again. The cancellation was not perfect, but it appeared this would so greatly reduce the net drift rates that the fuel would remain trapped long enough to heat it to the required temperatures.[12]

His 1958 description was simple and direct:

Magnetic confinement in the stellarator is based on a strong magnetic field produced by solenoidal coils encircling a toroidal tube. The configuration is characterized by a 'rotational transform', such that a single line of magnetic force, followed around the system, intersects a cross-sectional plane in points which successively rotate about the magnetic axis. ... A rotational transform may be generated either by a solenoidal field in a twisted, or figure-eight shaped, tube, or by the use of an additional transverse multipolar helical field, with helical symmetry.[13]

While working at Los Alamos in 1950, John Wheeler suggested setting up a secret research lab at Princeton University that would carry on theoretical work on H-bombs after he returned to the university in 1951. Spitzer was invited to join this program, given his previous research in interstellar plasmas.[14]

But by the time of his trip to Aspen, Spitzer had lost interest in bomb design and he turned his attention full-time to fusion as a power source.[15] Over the next few months, Spitzer produced a series of reports outlining the conceptual basis for the stellarator, as well as potential problems. The series is notable for its depth; it not only included a detailed analysis of the mathematics of the plasma and stability but also outlined a number of additional problems like heating the plasma and dealing with impurities.[16]

With this work in hand, Spitzer began to lobby the Department of Energy (DOE) for funding to develop the system.[16] He outlined a plan involving three stages. The first would see the construction of a Model A, whose purpose was to demonstrate that a plasma could be created and that its confinement time was better than a torus. If the A model was successful, the B model would attempt to heat the plasma to fusion temperatures. This would be followed by a C model, which would attempt to actually create fusion reactions at a large scale.[17] This entire series was expected to take about a decade.[18]

Around the same time, Jim Tuck had been introduced to the pinch concept while working at Clarendon Laboratory at Oxford University. He was offered a job in the US and eventually ended up at Los Alamos, where he acquainted the other researchers with the concept. When he heard Spitzer was promoting the stellarator, he also travelled to Washington to propose building a pinch device. He considered Spitzer's plans "incredibly ambitious." Nevertheless, Spitzer was successful in gaining $50,000 in funding from the DOE, while Tuck received nothing.[17]

The Princeton program was officially created on 1 July 1951. Spitzer, an avid mountain climber,[c] proposed the name "Project Matterhorn" because he felt "the work at hand seemed difficult, like the ascent of a mountain."[19] Two sections were initially set up, S Section working on the stellarator under Spitzer, and B Section working on bomb design under Wheeler. Matterhorn was set up at Princeton's new Forrestal Campus, a 825 acres (334 ha) plot of land the University purchased from the Rockefeller Institute for Medical Research when Rockefeller relocated to Manhattan.[d] The land was located about 3 miles (4.8 km) from the main Princeton campus and already had sixteen laboratory buildings. Spitzer set up the top-secret S Section in a former rabbit hutch.[20]

It was not long before the other labs began agitating for their own funding. Tuck had managed to arrange some funding for his Perhapsatron through some discretionary budgets at LANL, but other teams at LANL, Berkeley and Oak Ridge (ORNL) also presented their ideas. The DOE eventually organized a new department for all of these projects, becoming "Project Sherwood".[21]

With the funding from the DOE, Spitzer began work by inviting James Van Allen to join the group and set up an experimental program. Allen suggested starting with a small "tabletop" device. This led to the Model A design, which began construction in 1952. It was made from 5-centimetre (2.0 in) pyrex tubes about 350 cm (11.5 ft) in total length, and magnets capable of about 1,000 gauss.[22] The machine began operations in early 1953 and clearly demonstrated improved confinement over the simple torus.[23]

This led to the construction of the Model B, which had the problem that the magnets were not well mounted and tended to move around when they were powered to their maximum capacity of 50,000 gauss. A second design also failed for the same reason, but this machine demonstrated several-hundred-kilovolt X-rays that suggested good confinement. The lessons from these two designs led to the B-1, which used ohmic heating (see below) to reach plasma temperatures around 100,000 degrees.[23] This machine demonstrated that impurities in the plasma caused large x-ray emissions that rapidly cooled the plasma. In 1956, B-1 was rebuilt with an ultra-high vacuum system to reduce the impurities but found that even at smaller quantities they were still a serious problem. Another effect noticed in the B-1 was that during the heating process, the particles would remain confined for only a few tenths of a millisecond, while once the field was turned off, any remaining particles were confined for as long as 10 milliseconds. This appeared to be due to "cooperative effects" within the plasma.[24]

Meanwhile, a second machine known as B-2 was being built. This was similar to the B-1 machine but used pulsed power to allow it to reach higher magnetic energy and included a second heating system known as magnetic pumping. This machine was also modified to add an ultra-high vacuum system. Unfortunately, B-2 demonstrated little heating from the magnetic pumping, which was not entirely unexpected because this mechanism required longer confinement times, and this was not being achieved. As it appeared that little could be learned from this system in its current form, in 1958 it was sent to the Atoms for Peace show in Geneva.[24] However, when the heating system was modified, the coupling increased dramatically, demonstrating temperatures within the heating section as high as 1,000 electronvolts (160 aJ).[22][e]

Two additional machines were built to study pulsed operation. B-64 was completed in 1955, essentially a larger version of the B-1 machine but powered by pulses of current that produced up to 15,000 gauss. This machine included a diverter, which removed impurities from the plasma, greatly reducing the x-ray cooling effect seen on earlier machines. B-64 included straight sections in the curved ends which gave it a squared-off appearance. This appearance led to its name, it was a "figure-8, squared", or 8 squared, or 64. This led to experiments in 1956 where the machine was re-assembled without the twist in the tubes, allowing the particles to travel without rotation.[25]

B-65, completed in 1957, was built using the new "racetrack" layout. This was the result of the observation that adding helical coils to the curved portions of the device produced a field that introduced the rotation purely through the resulting magnetic fields. This had the added advantage that the magnetic field included shear, which was known to improve stability.[25] B-3, also completed in 1957, was a greatly enlarged B-2 machine with ultra-high vacuum and pulsed confinement up to 50,000 gauss and projected confinement times as long as 0.01 second. The last of the B-series machines was the B-66, completed in 1958, which was essentially a combination of the racetrack layout from B-65 with the larger size and energy of the B-3.[24]

Unfortunately, all of these larger machines demonstrated a problem that came to be known as "pump out". This effect was causing plasma drift rates that were not only higher than classical theory suggested but also much higher than the Bohm rates. B-3's drift rate was a full three times that of the worst-case Bohm predictions, and failed to maintain confinement for more than a few tens of microseconds.[25]

As early as 1954, as research continued on the B-series machines, the design of the Model C device was becoming more defined. It emerged as a large racetrack-layout machine with multiple heating sources and a diverter, essentially an even larger B-66. Construction began in 1958 and was completed in 1961. It could be adjusted to allow a plasma minor axis between 5 and 7.5 centimetres (2.0 and 3.0 in) and was 1,200 cm (470 in) in length. The toroidal field coils normally operated at 35,000 gauss.[25]

By the time Model C began operations, information collected from previous machines was making it clear that it would not be able to produce large-scale fusion. Ion transport across the magnetic field lines was much higher than classical theory suggested. Greatly increased magnetic fields of the later machines did little to address this, and confinement times simply were not improving. Attention began to turn to a much greater emphasis on the theoretical understanding of the plasma. In 1961, Melvin B. Gottlieb took over the Matterhorn Project from Spitzer, and on 1 February the project was renamed as the Princeton Plasma Physics Laboratory (PPPL).[20]

Continual modification and experimentation on the Model C slowly improved its operation, and the confinement times eventually increased to match that of Bohm predictions. New versions of the heating systems were used that slowly increased the temperatures. Notable among these was the 1964 addition of a small particle accelerator to accelerate fuel ions to high enough energy to cross the magnetic fields, depositing energy within the reactor when they collided with other ions already inside.[20] This method of heating, now known as neutral beam injection, has since become almost universal on magnetic confinement fusion machines.[26]

Model C spent most of its history involved in studies of ion transport.[20] Through continual tuning of the magnetic system and the addition of the new heating methods, in 1969, Model C eventually reached electron temperatures of 400 eV. Through this period, a number of new potential stellarator designs emerged, using a single set of magnetic coils. The Model C used separate confinement and helical coils, but it was seen that these could be combined, and this led to the torsitron concept.[27][f]

In 1968, scientists in the Soviet Union released the results of their tokamak machines, notably their newest example, T-3. The results were so startling that there was widespread scepticism. To address this, the Soviets invited a team of experts from the United Kingdom to test the machines for themselves. Their tests, made using a laser-based system developed for the ZETA reactor in England, verified the Soviet claims of electron temperatures of 1,000 eV. What followed was a "veritable stampede" of tokamak construction worldwide.[28]

At first the US labs ignored the tokamak; Spitzer himself dismissed it out of hand as experimental error. However, as new results came in, especially the UK reports, Princeton found itself in the position of trying to defend the stellarator as a useful experimental machine while other groups from around the US were clamoring for funds to build tokamaks. In July 1969 Gottlieb had a change of heart, offering to convert the Model C to a tokamak layout. In December it was shut down and reopened in May as the Symmetric Tokamak (ST).

The ST immediately matched the performance being seen in the Soviet machines, besting the Model C's results by over ten times. From that point, PPPL was the primary developer of the tokamak approach in the US, introducing a series of machines to test various designs and modifications. The Princeton Large Torus of 1975 quickly hit several performance numbers that were required for a commercial machine, and it was widely believed the critical threshold of breakeven would be reached in the early 1980s. What was needed was larger machines and more powerful systems to heat the plasma to fusion temperatures.

Tokamaks are a type of pinch machine, differing from earlier designs primarily in the amount of current in the plasma: above a certain threshold known as the safety factor, or q, the plasma is much more stable. ZETA ran at a q around ​1⁄3, while experiments on tokamaks demonstrated it needs to be at least 1. Machines following this rule showed dramatically improved performance. However, by the mid-1980s the easy path to fusion disappeared; as the amount of current in the new machines began to increase, a new set of instabilities in the plasma appeared. These could be addressed, but only by greatly increasing the power of the magnetic fields, requiring superconducting magnets and huge confinement volumes. The cost of such a machine was such that the involved parties banded together to begin the ITER project.

As the problems with the tokamak approach grew, there was renewed interest in the stellarator approach.[2] This coincided with the development of advanced computer aided design tools that allowed the construction of complex magnets that were previously known but considered too difficult to design and build.

The lack of an internal current eliminates some of the instabilities of the tokamak, meaning the stellarator should be more stable at similar operating conditions. On the downside, since no confinement is provided by the current found in a tokamak, the stellarator requires more powerful magnets to reach any given confinement. The stellarator is an inherently steady-state machine, which has several advantages from an engineering standpoint.

Heating a gas increases the energy of the particles within it, so by heating a gas into the hundreds of millions of degrees, the majority of the particles within it would reach the energy required to fuse. According to the Maxwell–Boltzmann distribution, some of the particles will reach the required energies at much lower average temperatures. Because the energy released by the reaction is much greater than what it takes to start it, even a small number of reactions can heat surrounding fuel until it fuses as well. In 1944, Enrico Fermi calculated the D-T reaction would be self-sustaining at about 50,000,000 degrees Celsius (90,000,000 degrees Fahrenheit).[29]

Materials heated beyond a few tens of thousand degrees ionize into their electrons and nuclei, producing a gas-like state of matter known as plasma. According to the ideal gas law, like any hot gas, plasma has an internal pressure and thus wants to expand.[30] For a fusion reactor, the challenge is to keep the plasma contained; any known substance would melt at these temperatures. But because a plasma is electrically conductive, it is subject to electric and magnetic fields. In a magnetic field, the electrons and nuclei orbit around the magnetic field lines, confining them to the area defined by the field.[31][32]

A simple confinement system can be made by placing a tube inside the open core of a solenoid. The tube can be evacuated and then filled with the requisite gas and heated until it becomes a plasma. The plasma naturally wants to expand outwards to the walls of the tube, as well as move along it, towards the ends. The solenoid creates magnetic field lines running down the center of the tube, and the plasma particles orbit these lines, preventing their motion towards the sides. Unfortunately, this arrangement would not confine the plasma along the length of the tube, and the plasma would be free to flow out the ends.[33]

The obvious solution to this problem is to bend the tube around into a torus (a ring or donut) shape.[33] Motion towards the sides remains constrained as before, and while the particles remain free to move along the lines, in this case, they will simply circulate around the long axis of the tube. But, as Fermi pointed out,[g] when the solenoid is bent into a ring, the electrical windings would be closer together on the inside than the outside. This would lead to an uneven field across the tube, and the fuel will slowly drift out of the center. Since the electrons and ions would drift in opposite directions, this would lead to a charge separation and electrostatic forces that would eventually overwhelm the magnetic force. Some additional force needs to counteract this drift, providing long-term confinement.[6][33]

Spitzer's key concept in the stellarator design is that the drift that Fermi noted could be canceled out through the physical arrangement of the vacuum tube. In a simple torus, particles on the inside edge of the tube, where the field was stronger, would drift up, while those on the outside would drift down (or vice versa). However, if the particle were made to alternate between the inside and outside of the tube, the drifts would cancel out. The cancellation is not perfect, leaving some net drift, but basic calculations suggested drift would be lowered enough to confine plasma long enough to heat it sufficiently.

Spitzer's suggestion for doing this was simple. Instead of a normal torus, the device would essentially be cut in half to produce two half-tori. They would then be joined with two straight sections between the open ends. The key was that they were connected to alternate ends so that the right half of one of the tori was connected to the left of the other. The resulting design resembled a figure-8 when viewed from above. Because the straight tubes could not pass through each other, the design did not lay flat, the tori at either end had to be tilted. This meant the drift cancellation was further reduced, but again, calculations suggested the system would work.

To understand how the system works to counteract drift, consider the path of a single particle in the system starting in one of the straight sections. If that particle is perfectly centered in the tube, it will travel down the center into one of the half-tori, exit into the center of the next tube, and so on. This particle will complete a loop around the entire reactor without leaving the center. Now consider another particle traveling parallel to the first, but initially located near the inside wall of the tube. In this case, it will enter the outside edge of the half-torus and begin to drift down. It exits that section and enters the second straight section, still on the outside edge of that tube. However, because the tubes are crossed, when it reaches the second half-torus it enters it on the inside edge. As it travels through this section it drifts back up.

This effect would reduce one of the primary causes of drift in the machine, but there were others to consider as well. Although the ions and electrons in the plasma would both circle the magnetic lines, they would do so in opposite directions, and at very high rotational speeds. This leads to the possibility of collisions between particles circling different lines of force as they circulate through the reactor, which due to purely geometric reasons, causes the fuel to slowly drift outward. This process eventually causes the fuel to either collide with the structure or cause a large charge separation between the ions and electrons. Spitzer introduced the concept of a divertor, a magnet placed around the tube that pulled off the very outer layer of the plasma. This would remove the ions before they drifted too far and hit the walls. It would also remove any heavier elements in the plasma.

Using "classical" calculations the rate of diffusion through collisions was low enough that it would be much lower than the drift due to uneven fields in a normal toroid. But studies in 1949 demonstrated much higher losses and became known as Bohm diffusion. Spitzer spent considerable effort considering this issue, and concluded that the anomalous rate being seen by Bohm was due to instability in the plasma, which he believed could be addressed.[35]

Practical complications make the original figure-8 device less than ideal. This led to alternative designs and additions.

One of the major concerns is that the magnetic fields in the system will only properly confine a particle of a given mass traveling at a given speed. Particles traveling faster or slower will not circulate in the desired fashion. Particles with very low speeds (corresponding to low temperatures) are not be confined and can drift out to the tube walls. Those with too much energy may hit the outside walls of the curved sections. To address these concerns, Spitzer introduced the concept of a divertor that would connect to one of the straight sections. This was essentially a mass spectrometer that would remove particles that were moving too fast or too slow for proper confinement.

The physical limitation that the two straight sections cannot intersect means that the rotational transform within the loop is not a perfect 180 degrees, but typically closer to 135 degrees. This led to alternate designs in an effort to get the angle closer to 180. An early attempt was built into the Stellarator B-2, which placed both curved sections flat in relation to the ground, but at different heights. The formerly straight sections had additional curves inserted, two sections of about 45 degrees, so they now formed extended S-shapes. This allowed them to route around each other while being perfectly symmetrical in terms of angles.

A better solution to the need to rotate the particles was introduced in the Stellarator B-64 and B-65. These eliminated the cross-over and flattened the device into an oval, or as they referred to it, a racetrack. The rotation of the particles was introduced by placing a new set of magnetic coils on the half-torus on either end, the corkscrew windings. The field from these coils mixes with the original confinement fields to produce a mixed field that rotates the lines of force through 180 degrees. This made the mechanical design of the reactor much simpler, but in practice, it was found that the mixed field was very difficult to produce in a perfectly symmetrical fashion.

Unlike the z-pinch designs being explored in the UK and other US labs, the stellarator has no induced electrical current within the plasma - at a macroscopic level, the plasma is neutral and unmoving, in spite of the individual particles within it rapidly circulating. In pinch machines, and the later tokamaks, the current itself is one of the primary methods of heating the plasma. In the stellarator, no such natural heating source is present.

Early stellarator designs used a system similar to those in the pinch devices to provide the initial heating to bring the gas to plasma temperatures. This consisted of a single set of windings from a transformer, with the plasma itself forming the secondary set. When energized with a pulse of current, the particles in the region are rapidly energized and begin to move. This brings additional gas into the region, quickly ionizing the entire mass of gas. This concept was referred to as ohmic heating because it relied on the resistance of the gas to create heat, in a fashion not unlike a conventional resistance heater. As the temperature of the gas increases, the conductivity of the plasma improves. This makes the ohmic heating process less and less effective, and this system is limited to temperatures of about 1 million kelvins.[36]

To heat the plasma to higher temperatures, a second heat source was added, the magnetic pumping system. This consisted of radio-frequency source fed through a coil spread along the vacuum chamber. The frequency is chosen to be similar to the natural frequency of the particles around the magnetic lines of force, the cyclotron frequency. This causes the particles in the area to gain energy, which causes them to orbit in a wider radius. Since other particles are orbiting their own lines nearby, at a macroscopic level, this change in energy appears as an increase in pressure.[37] According to the ideal gas law, this results in an increase in temperature. Like the ohmic heating, this process also becomes less efficient as the temperature increases, but is still capable of creating very high temperatures. When the frequency is deliberately set close to that of the ion circulation, this is known as ion-cycloron resonance heating,[38] although this name is not widely used.

There are several ways to heat the plasma (which must be done before ignition can occur).

Current heating

The plasma is electrically conductive, and heats up when a current is passed through it (due to electrical resistance). Only used for initial heating, as the resistance is inversely proportional to the plasma temperature.

High-frequency electromagnetic waves

The plasma absorbs energy when electromagnetic waves are applied to it (in the same manner as food in a microwave).

Heating by neutral particles

A neutral particle beam injector makes ions and accelerates them with an electric field. To avoid being affected by the Stellarator's magnetic field, the ions must be neutralised. Neutralised ions are then injected into the plasma. Their high kinetic energy is transferred to the plasma particles by collisions, heating them.

The original figure-8 design that used geometry to produce the rotational transform of the magnetic fields.

Classical stellarator

A toroidal or racetrack-shaped design with separate helical coils on either end to produce the rotation.

Torsatron

A stellarator with continuous helical coils. It can also have the continuous coils replaced by a number of discrete coils producing a similar field.

Heliotron

A stellarator in which a helical coil is used to confine the plasma, together with a pair of poloidal field coils to provide a vertical field. Toroidal field coils can also be used to control the magnetic surface characteristics. The Large Helical Device in Japan uses this configuration.

A helical axis stellarator, in which the magnetic axis (and plasma) follows a helical path to form a toroidal helix rather than a simple ring shape. The twisted plasma induces twist in the magnetic field lines to effect drift cancellation, and typically can provide more twist than the Torsatron or Heliotron, especially near the centre of the plasma (magnetic axis). The original Heliac consists only of circular coils, and the flexible heliac[40] (H-1NF, TJ-II, TU-Heliac) adds a small helical coil to allow the twist to be varied by a factor of up to 2.

Helias

A helical advanced stellarator, using an optimized modular coil set designed to simultaneously achieve high plasma, low Pfirsch–Schluter currents and good confinement of energetic particles; i.e., alpha particles for reactor scenarios.[41] The Helias has been proposed to be the most promising stellarator concept for a power plant, with a modular engineering design and optimised plasma, MHD and magnetic field properties.[citation needed] The Wendelstein 7-X device is based on a five field-period Helias configuration.

The goal of magnetic confinement devices is to minimise energy transport across a magnetic field. Toroidal devices are relatively successful because the magnetic properties seen by the particles are averaged as they travel around the torus. The strength of the field seen by a particle, however, generally varies, so that some particles will be trapped by the mirror effect. These particles will not be able to average the magnetic properties so effectively, which will result in increased energy transport. In most stellarators, these changes in field strength are greater than in tokamaks, which is a major reason that transport in stellarators tends to be higher than in tokamaks.

University of Wisconsin electrical engineering Professor David Anderson and research assistant John Canik proved in 2007 that the Helically Symmetric eXperiment (HSX) can overcome this major barrier in plasma research. The HSX is the first stellarator to use a quasisymmetric magnetic field. The team designed and built the HSX with the prediction that quasisymmetry would reduce energy transport. As the team's latest research showed, that is exactly what it does. "This is the first demonstration that quasisymmetry works, and you can actually measure the reduction in transport that you get," says Canik.[42][43]

The newer Wendelstein 7-X in Germany was designed to be close to omnigeneity (a property of the magnetic field such that the mean radial drift is zero), which is a necessary but not sufficient condition for quasisymmetry;[44] that is, all quasisymmetric magnetic fields are omnigenous, but not all omnigenous magnetic fields are quasisymmetric.

1.
Wendelstein 7-X
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The Wendelstein 7-X reactor is an experimental stellarator built in Greifswald, Germany, by the Max Planck Institute of Plasma Physics, and completed in October 2015. As of 2015, the Wendelstein 7-X reactor was the largest stellarator device and it is planned, circa 2021, to operate with up to 30 minutes of continuous plasma discharge, demonstrating an essential feature of a future power plant, continuous operation. The research facility is an independent partner project with the University of Greifswald, the Wendelstein 7-X device is based on a five field-period Helias configuration. The 50 non-planar coils are used for adjusting the magnetic field and it aims for a plasma density of 3×1020 particles per cubic metre, and a plasma temperature of 60–130 megakelvin. The main components are the coils, cryostat, plasma vessel, divertor. The coils are arranged around a heat insulating cladding with a diameter of 16 meters, a cooling device produces enough liquid helium to cool down the magnets and their enclosure to superconductivity temperature. The coils will carry 12.8 kA current and create a field of up to 3 teslas, the plasma vessel, built of 20 parts, is on the inside, adjusted to the complex shape of the magnetic field. It has 254 ports for plasma heating and observation diagnostics, the whole plant is built of five almost identical modules, which were assembled in the experiment hall. The heating system includes 10 megawatts of microwaves for Electron Cyclotron Resonance Heating, for up to 10 seconds, an Ion Cyclotron Resonance Heating system will become available for physics operation in OP1.2. The German funding arrangement for the project was negotiated in 1994 and its new building was completed in 2000. Construction of the stellarator was originally expected to reach completion in 2006, problems with the coils took about 3 years to fix. The schedule slipped into late 2015, a three-lab American consortium became a partner in the project, paying $7.5 million USD of the eventual total cost of 1.06 billion Euros. In 2012, Princeton University and the Max Planck Society announced a new joint research center in plasma physics, the end of the construction phase was officially marked by an inauguration ceremony on 20 May 2014. After a period of vessel leak-checking, beginning in the summer of 2014, the cryostat was evacuated, the reactor successfully produced helium plasma for about 0.1 s on December 10,2015. For this initial test with about 1 mg of helium gas injected into the plasma vessel. Then on February 3,2016, operational phase 1 began, the highest temperature plasmas were produced by four megawatt microwave heater pulses lasting one second, Plasma electron temperatures reached 100 MK, while ion temperatures reached 10 MK. More than 2,000 pulses were conducted before shutdown, then the science program will continue while gradually increasing discharge power and duration. The special magnetic field topology was confirmed in 2016, financial support for the project is about 80% from Germany and about 20% from the European Union

2.
Greifswald
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Greifswald, officially the University and Hanseatic City of Greifswald, is a city in northeastern Germany. It is situated in the state of Mecklenburg-Vorpommern, at a distance of about 250 kilometres from Germanys two largest cities, Berlin and Hamburg, and 80 km from the Polish border. The town flanks the Baltic Sea, and is crossed by a small river and it is also located near Germanys two largest islands, Rügen and Usedom, and it is close to three of Germanys 14 national parks. It has been the capital of the newly established district of Vorpommern-Greifswald since the September 2011 district reforms, together with Stralsund, Greifswald forms one of four high-level urban centers of Mecklenburg-Vorpommern. The citys population was listed at 55,659 in 2013, Greifswald draws international attention due to the university, its surrounding BioCon Valley, the Nord Stream gas pipeline and the Wendelstein 7-X nuclear fusion projects. Greifswald is located in the northeast of Germany, approximately equidistant from Germanys two largest islands, Rügen and Usedom, the town is situated at the south end of the Bay of Greifswald, the historic centre being about 5 kilometres up the river Ryck that crosses the town. The area around Greifswald is mainly flat, and hardly more than 20 metres above sea level. Two islands, Koos and Riems, are part of Greifswald. Three of Germanys fourteen national parks can be reached by car in one hour or less from Greifswald, Greifswald is also roughly equidistant from Germanys two largest cities, Berlin and Hamburg. The nearest larger towns are Stralsund and Rostock, the coastal part of Greifswald at the mouth of the Ryck, named Greifswald-Wieck, evolved from a fishing village. Today it provides a beach, a marina and the main port for Greifswald. Greifswald was founded in 1199 when Cistercian monks founded the Eldena Abbey, in 1250, Wartislaw III, Duke of Pomerania, granted town privileges to Greifswald according to the Lübeck law. In 1199, the Rugian Prince Jaromar I allowed Danish Cistercian monks to build Hilda Abbey, now Eldena Abbey, at the mouth of the River Ryck. Among the lands granted the monks was a salt evaporation pond a short way up the river. This site was named Grypswold, which is the Low German precursor of the modern name – which means Griffins Forest. Legend says the monks were shown the best site for settlement by a mighty griffin living in a tree that grew on what became Greifswalds oldest street. The towns construction followed a scheme of streets, with church. It was settled primarily by Germans in the course of the Ostsiedlung, the salt trade helped Eldena Abbey to become an influential religious center, and Greifswald became a widely known market

3.
Plasma (physics)
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Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas. Yet unlike these three states of matter, plasma does not naturally exist on the Earth under normal surface conditions, the term was first introduced by chemist Irving Langmuir in the 1920s. However, true plasma production is from the separation of these ions and electrons that produces an electric field. Based on the environmental temperature and density either partially ionised or fully ionised forms of plasma may be produced. The positive charge in ions is achieved by stripping away electrons from atomic nuclei, the number of electrons removed is related to either the increase in temperature or the local density of other ionised matter. Plasma may be the most abundant form of matter in the universe, although this is currently tentative based on the existence. Plasma is mostly associated with the Sun and stars, extending to the rarefied intracluster medium, Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879. The nature of the Crookes tube cathode ray matter was identified by British physicist Sir J. J. The term plasma was coined by Irving Langmuir in 1928, perhaps because the glowing discharge molds itself to the shape of the Crookes tube and we shall use the name plasma to describe this region containing balanced charges of ions and electrons. Plasma is a neutral medium of unbound positive and negative particles. Although these particles are unbound, they are not ‘free’ in the sense of not experiencing forces, in turn this governs collective behavior with many degrees of variation. The average number of particles in the Debye sphere is given by the plasma parameter, bulk interactions, The Debye screening length is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, when this criterion is satisfied, the plasma is quasineutral. Plasma frequency, The electron plasma frequency is compared to the electron-neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics, for plasma to exist, ionization is necessary. The term plasma density by itself refers to the electron density, that is. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma. The degree of ionization, α, is defined as α = n i n i + n n, where n i is the number density of ions and n n is the number density of neutral atoms

4.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world

5.
Magnetic mirror
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A magnetic mirror is a type of magnetic confinement device, used in physics experiments to trap high temperature plasma using magnetic fields. This mirror effect will occur for particles within a limited range of velocities and angles of approach. Large experimental magnetic mirror machines have developed to confine hot deuterium plasma as a possible approach to fusion power. The largest machine that has built was the Mirror Fusion Test Facility completed in 1986 at Lawrence Livermore Laboratory in the US. Mirror research continues today in countries like Russia, a charged particle moving within a region of magnetic field experiences a Lorentz force that causes it to move in a helical path along a magnetic field line. The radius of the circle that the particle describes is called the radius of gyration or gyroradius and it is this force that can reflect the particle, causing it to decelerate and reverse direction. The concept of plasma confinement was proposed in mid-1950s independently by Gersh Budker at the Kurchatov Institute, Russia. Post at the Lawrence Livermore National Laboratory, the first small-scale open magnetic plasma trap machine was built in 1959 at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. By the late 1960s, magnetic mirror confinement was considered a technique for producing fusion energy. In the United States, еfforts were initially funded under the United States Atomic Energy Commissions Project Sherwood, a machine design was first published in 1967. The concept was advocated by Richard F. Post, Kenneth Fowler, Fred Coensgen, as a result of advocacy, the cold war, and the 1970s energy crisis a massive magnetic mirror program was funded by the U. S. federal government. These machines were built and tested at Livermore from the late 60s to the mid 80s, a number of institutions collaborated on these machines, conducting experiments. These included the Institute for Advanced Study and the University of Wisconsin–Madison, the last machine, the Mirror Fusion Test Facility was 372 million dollars, at that time, the most expensive project in Livermore history. It opened on February 21,1986 and was shut down. The reason given was to balance the United States federal budget and this program was supported from within the Carter and early Reagan administrations by Edwin E. Kintner, a U. S. Navy captain, under Alvin Trivelpiece. Kintner resigned in 1982 complaining that the government had not provided the resources needed for the research. Magnetic mirror research continued in Russia, one example is the Gas Dynamic Trap. This machine has achieved a 0.6 beta ratio for 5E-3 seconds, the concept had a number of technical challenges including maintaining the non-Maxwellian velocity distribution

6.
Princeton University
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Princeton University is a private Ivy League research university in Princeton, New Jersey, United States. The institution moved to Newark in 1747, then to the current site nine years later, Princeton provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences, and engineering. The university has ties with the Institute for Advanced Study, Princeton Theological Seminary, Princeton has the largest endowment per student in the United States. The university has graduated many notable alumni, two U. S. Presidents,12 U. S. Supreme Court Justices, and numerous living billionaires and foreign heads of state are all counted among Princetons alumni body. New Light Presbyterians founded the College of New Jersey in 1746 in order to train ministers, the college was the educational and religious capital of Scots-Irish America. In 1754, trustees of the College of New Jersey suggested that, in recognition of Governors interest, gov. Jonathan Belcher replied, What a name that would be. In 1756, the moved to Princeton, New Jersey. Its home in Princeton was Nassau Hall, named for the royal House of Orange-Nassau of William III of England, following the untimely deaths of Princetons first five presidents, John Witherspoon became president in 1768 and remained in that office until his death in 1794. During his presidency, Witherspoon shifted the focus from training ministers to preparing a new generation for leadership in the new American nation. To this end, he tightened academic standards and solicited investment in the college, in 1812, the eighth president the College of New Jersey, Ashbel Green, helped establish the Princeton Theological Seminary next door. The plan to extend the theological curriculum met with approval on the part of the authorities at the College of New Jersey. Today, Princeton University and Princeton Theological Seminary maintain separate institutions with ties that include such as cross-registration. Before the construction of Stanhope Hall in 1803, Nassau Hall was the sole building. The cornerstone of the building was laid on September 17,1754, during the summer of 1783, the Continental Congress met in Nassau Hall, making Princeton the countrys capital for four months. The class of 1879 donated twin lion sculptures that flanked the entrance until 1911, Nassau Halls bell rang after the halls construction, however, the fire of 1802 melted it. The bell was then recast and melted again in the fire of 1855, James McCosh took office as the colleges president in 1868 and lifted the institution out of a low period that had been brought about by the American Civil War. McCosh Hall is named in his honor, in 1879, the first thesis for a Doctor of Philosophy Ph. D. was submitted by James F. Williamson, Class of 1877. In 1896, the officially changed its name from the College of New Jersey to Princeton University to honor the town in which it resides

7.
Tokamak
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A tokamak is a device that uses a powerful magnetic field to confine plasma in the shape of a torus. Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape, such a helical field can be generated by adding a toroidal field and a poloidal field. In a tokamak, the field is produced by electromagnets that surround the torus. This current is induced inside the plasma with a set of electromagnets. The tokamak is one of several types of magnetic confinement devices and it is the leading candidate for a practical fusion reactor. Magnetic fields are used for confinement since no material could withstand the extremely high temperature of the plasma. The worlds largest tokamak project is the ITER being constructed in Saint-Paul-lès-Durance, scheduled to begin operation in 2020, it is expected to produce an output power of 500 megawatts. Tokamaks were invented in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, although nuclear fusion research began soon after World War II, the programs in various countries were each initially classified as secret. Experimental research of tokamak systems started in 1956 in Kurchatov Institute, the group constructed the first tokamaks, the most successful being T-3 and its larger version T-4. T-4 was tested in 1968 in Novosibirsk, conducting the first ever quasistationary thermonuclear fusion reaction, in 1973 design work on JET, the Joint European Torus, began. Positively and negatively charged ions and negatively charged electrons in a plasma are at very high temperatures. In order to maintain the process, particles from the hot plasma must be confined in the central region. Magnetic confinement fusion devices exploit the fact that particles in a magnetic field experience a Lorentz force. Early fusion research devices were variants on the Z-pinch and used electric current to generate a magnetic field to contain the plasma along a linear axis between two points. Researchers discovered that a simple toroidal field, in which the field lines run in circles around an axis of symmetry. This can be understood by looking at the orbits of individual particles, the particles not only spiral around the field lines, they also drift across the field. Since a toroidal field is curved and decreases in strength moving away from the axis of rotation, the ions and the electrons move parallel to the axis, the charge separation leads to an electric field and an additional drift, in this case outward for both ions and electrons. Alternatively, the plasma can be viewed as a torus of fluid with a magnetic field frozen in, the plasma pressure results in a force that tends to expand the torus

8.
Mark Oliphant
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Born and raised in Adelaide, South Australia, Oliphant graduated from the University of Adelaide in 1922. There, he used a particle accelerator to fire heavy hydrogen nuclei at various targets and he discovered the nuclei of helium-3 and tritium. He also discovered that when they reacted with other, the particles that were released had far more energy than they started with. Energy had been liberated from inside the nucleus, and he realised that this was a result of nuclear fusion, Oliphant left the Cavendish Laboratory in 1937 to become the Poynting Professor of Physics at the University of Birmingham. He attempted to build a 60-inch cyclotron at the university, and he became involved with the development of radar, heading a group at the University of Birmingham that included John Randall and Harry Boot. They created a new design, the cavity magnetron, that made microwave radar possible. Oliphant also formed part of the MAUD Committee, which reported in July 1941, that a bomb was not only feasible. Oliphant was instrumental in spreading the word of this finding in the United States, later in the war, he worked on it with his friend Ernest Lawrence at the Radiation Laboratory in Berkeley, California, developing electromagnetic isotope separation. He retired in 1976, but was appointed Governor of South Australia on the advice of Premier and he assisted in the founding of the Australian Democrats political party, and he was the chairman of the meeting in Melbourne in 1977 at which the party was launched. Late in life he watched his wife, Rosa, suffer before her death in 1987 and he died in Canberra in 2000. Marcus Mark Laurence Elwin Oliphant was born on 8 October 1901 in Kent Town and his mother was Beatrice Edith Fanny Oliphant, née Tucker, an artist. He was named after Marcus Clarke, the Australian author, and Laurence Oliphant, most people called him Mark, this became official when he was knighted in 1959. He had four brothers, Roland, Keith, Nigel. His parents were theosophists, and as such were opposed to eating meat, Marcus became a lifelong vegetarian while a boy, after witnessing the slaughter of pigs on a farm. He was found to be deaf in one ear and he needed glasses for severe astigmatism. Oliphant was first educated at schools in Goodwood and Mylor. He attended Unley High School in Adelaide, and, for his year in 1918. After graduation he failed to obtain a bursary to attend university and he then got a cadetship with the State Library of South Australia, which allowed him to take courses at the University of Adelaide at night

9.
Ernest Rutherford
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Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS was a New Zealand-born British physicist who came to be known as the father of nuclear physics. Encyclopædia Britannica considers him to be the greatest experimentalist since Michael Faraday and this work was done at McGill University in Canada. Rutherford moved in 1907 to the Victoria University of Manchester in the UK, Rutherford performed his most famous work after he became a Nobel laureate. He conducted research that led to the first splitting of the atom in 1917 in a reaction between nitrogen and alpha particles, in which he also discovered the proton. Rutherford became Director of the Cavendish Laboratory at the University of Cambridge in 1919, after his death in 1937, he was honoured by being interred with the greatest scientists of the United Kingdom, near Sir Isaac Newtons tomb in Westminster Abbey. The chemical element rutherfordium was named after him in 1997, Ernest Rutherford was the son of James Rutherford, a farmer, and his wife Martha Thompson, originally from Hornchurch, Essex, England. James had emigrated to New Zealand from Perth, Scotland, to raise a little flax, Ernest was born at Brightwater, near Nelson, New Zealand. His first name was mistakenly spelled Earnest when his birth was registered, Rutherfords mother Martha Thompson was a schoolteacher. He studied at Havelock School and then Nelson College and won a scholarship to study at Canterbury College, University of New Zealand, in 1898 Thomson recommended Rutherford for a position at McGill University in Montreal, Canada. He was to replace Hugh Longbourne Callendar who held the chair of Macdonald Professor of physics and was coming to Cambridge, in 1901 he gained a DSc from the University of New Zealand. In 1907 Rutherford returned to Britain to take the chair of physics at the Victoria University of Manchester, during World War I, he worked on a top secret project to solve the practical problems of submarine detection by sonar. In 1916 he was awarded the Hector Memorial Medal, in 1919 he returned to the Cavendish succeeding J. J. Thomson as the Cavendish professor and Director. Between 1925 and 1930 he served as President of the Royal Society, in 1933, Rutherford was one of the two inaugural recipients of the T. K. Sidey Medal, set up by the Royal Society of New Zealand as an award for outstanding scientific research. For some time before his death, Rutherford had a hernia, which he had neglected to have fixed. Despite an emergency operation in London, he died four days afterwards of what physicians termed intestinal paralysis, after cremation at Golders Green Crematorium, he was given the high honour of burial in Westminster Abbey, near Isaac Newton and other illustrious British scientists. At Cambridge, Rutherford started to work with J. J. Thomson on the effects of X-rays on gases. Hearing of Becquerels experience with uranium, Rutherford started to explore its radioactivity, continuing his research in Canada, he coined the terms alpha ray and beta ray in 1899 to describe the two distinct types of radiation. He then discovered that thorium gave off a gas which produced an emanation which was itself radioactive and he found that a sample of this radioactive material of any size invariably took the same amount of time for half the sample to decay – its half-life

10.
Particle accelerator
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A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in physics as colliders, or as synchrotron light sources for the study of condensed matter physics. There are currently more than 30,000 accelerators in operation around the world, there are two basic classes of accelerators, electrostatic and electrodynamic accelerators. Electrostatic accelerators use electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator, a small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields to accelerate particles. Since in these types the particles can pass through the accelerating field multiple times. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators, because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general. Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research and it has been estimated that there are approximately 30,000 accelerators worldwide. The bar graph shows the breakdown of the number of industrial accelerators according to their applications, for the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles, leptons and quarks for the matter, the largest and highest energy particle accelerator used for elementary particle physics is the Large Hadron Collider at CERN, operating since 2009. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon, the largest such particle accelerator is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. An example of type of machine is LANSCE at Los Alamos. A large number of light sources exist worldwide. The ESRF in Grenoble, France has been used to extract detailed 3-dimensional images of trapped in amber. Thus there is a demand for electron accelerators of moderate energy. Everyday examples of particle accelerators are cathode ray tubes found in television sets and these low-energy accelerators use a single pair of electrodes with a DC voltage of a few thousand volts between them

11.
Deuterium
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Deuterium is one of two stable isotopes of hydrogen. The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, Deuterium has a natural abundance in Earths oceans of about one atom in 6420 of hydrogen. Thus deuterium accounts for approximately 0. 0156% of all the naturally occurring hydrogen in the oceans, the abundance of deuterium changes slightly from one kind of natural water to another. The deuterium isotopes name is formed from the Greek deuteros meaning second, Deuterium was discovered and named in 1931 by Harold Urey. When the neutron was discovered in 1932, this made the structure of deuterium obvious. Soon after deuteriums discovery, Urey and others produced samples of water in which the deuterium content had been highly concentrated. Deuterium is destroyed in the interiors of stars faster than it is produced, other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the Big Bang 13.8 billion years ago and this is the ratio found in the gas giant planets, such as Jupiter. However, other bodies are found to have different ratios of deuterium to hydrogen-1. This is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets, like the water-cycle in Earths weather, such heating processes may enrich deuterium with respect to protium. The analysis of ratios in comets found results very similar to the mean ratio in Earths oceans. This reinforces theories that much of Earths ocean water is of cometary origin, the deuterium/protium ratio of the comet 67P/Churyumov-Gerasimenko, as measured by the Rosetta space probe, is about three times that of earth water. This figure is the highest yet measured in a comet, deuterium/protium ratios thus continue to be an active topic of research in both astronomy and climatology. Deuterium is frequently represented by the chemical symbol D, since it is an isotope of hydrogen with mass number 2, it is also represented by 2H. IUPAC allows both D and 2H, although 2H is preferred, a distinct chemical symbol is used for convenience because of the isotopes common use in various scientific processes. In quantum mechanics the energy levels of electrons in atoms depend on the mass of the system of electron. For hydrogen, this amount is about 1837/1836, or 1.000545, the energies of spectroscopic lines for deuterium and light-hydrogen therefore differ by the ratios of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the lines of light hydrogen

12.
Lithium
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Lithium is a chemical element with the symbol Li and atomic number 3. It is a soft, silver-white metal belonging to the metal group of chemical elements. Under standard conditions, it is the lightest metal and the least dense solid element, like all alkali metals, lithium is highly reactive and flammable. For this reason, it is stored in mineral oil. When cut open, it exhibits a metallic luster, but contact with moist air corrodes the surface quickly to a silvery gray. Because of its reactivity, lithium never occurs freely in nature, and instead, appears only in compounds. Lithium occurs in a number of minerals, but due to its solubility as an ion, is present in ocean water and is commonly obtained from brines. On a commercial scale, lithium is isolated electrolytically from a mixture of lithium chloride, the nucleus of the lithium atom verges on instability, since the two stable lithium isotopes found in nature have among the lowest binding energies per nucleon of all stable nuclides. Because of its relative instability, lithium is less common in the solar system than 25 of the first 32 chemical elements even though the nuclei are very light in atomic weight. For related reasons, lithium has important links to nuclear physics, the transmutation of lithium atoms to helium in 1932 was the first fully man-made nuclear reaction, and lithium-6 deuteride serves as a fusion fuel in staged thermonuclear weapons. These uses consume more than three quarters of lithium production, Lithium is found in variable amounts in foods, primary food sources are grains and vegetables, in some areas, the drinking water also provides significant amounts of the element. Human dietary lithium intakes depend on location and the type of foods consumed, traces of lithium were detected in human organs and fetal tissues already in the late 19th century, leading to early suggestions as to possible specific functions in the organism. However, it took another century until evidence for the essentiality of lithium became available, in studies conducted from the 1970s to the 1990s, rats and goats maintained on low-lithium rations were shown to exhibit higher mortalities as well as reproductive and behavioral abnormalities. Lithium appears to play an important role during the early fetal development as evidenced by the high lithium contents of the embryo during the early gestational period. The available experimental evidence now appears to be sufficient to accept lithium as essential, the lithium ion Li+ administered as any of several lithium salts has proven to be useful as a mood-stabilizing drug in the treatment of bipolar disorder in humans. Like the other metals, lithium has a single valence electron that is easily given up to form a cation. Because of this, lithium is a conductor of heat and electricity as well as a highly reactive element. Lithiums low reactivity is due to the proximity of its electron to its nucleus

A magnetic mirror, known as a magnetic trap in Russia, is a type of magnetic confinement device used in fusion power to …

This shows a basic magnetic mirror machine including a charged particle's motion. The rings in the centre extend the confinement area horizontally, but are not strictly needed and are not found on many mirror machines.

Deuterium (or hydrogen-2, symbol D or 2H, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the …

Deuterium discharge tube

Ionized deuterium in a fusor reactor giving off its characteristic pinkish-red glow

Harold Urey

A view of the Sausage device casing of the Ivy Mikehydrogen bomb, with its instrumentation and cryogenic equipment attached. This bomb held a cryogenic Dewar flask containing room for as much as 160 kilograms of liquid deuterium. The bomb was 20 feet tall. Note the seated man at the right of the photo for the scale.